intrusive_list: Add pop_back(), pop_front(), front(), and back() member functions

src/common/intrusive_list.h

@@ -87,6 +87,24 @@ public:
         insert(end(), node);
     }
 
+    /**
+     * Erases the node at the front of the list.
+     * @note Must not be called on an empty list.
+     */
+    void pop_front() {
+        DEBUG_ASSERT(!empty());
+        erase(begin());
+    }
+
+    /**
+     * Erases the node at the back of the list.
+     * @note Must not be called on an empty list.
+     */
+    void pop_back() {
+        DEBUG_ASSERT(!empty());
+        erase(--end());
+    }
+
     /**
      * Removes node from list
      * @param node Node to remove from list.
@@ -103,6 +121,42 @@ public:
         return root->next == root.get();
     }
 
+    /**
+     * Retrieves a reference to the node at the front of the list.
+     * @note Must not be called on an empty list.
+     */
+    reference front() {
+        DEBUG_ASSERT(!empty());
+        return *begin();
+    }
+
+    /**
+     * Retrieves a constant reference to the node at the front of the list.
+     * @note Must not be called on an empty list.
+     */
+    const_reference front() const {
+        DEBUG_ASSERT(!empty());
+        return *begin();
+    }
+
+    /**
+     * Retrieves a reference to the node at the back of the list.
+     * @note Must not be called on an empty list.
+     */
+    reference back() {
+        DEBUG_ASSERT(!empty());
+        return *--end();
+    }
+
+    /**
+     * Retrieves a constant reference to the node at the back of the list.
+     * @note Must not be called on an empty list.
+     */
+    const_reference back() const {
+        DEBUG_ASSERT(!empty());
+        return *--end();
+    }
+
     // Iterator interface
     iterator               begin()         { return iterator(root.get(), root->next);       }
     const_iterator         begin()   const { return const_iterator(root.get(), root->next); }